The present invention relates to an optical information record carrier of the type comprising upper and lower optical disks, each with an optical recording surface facing the other, and an annular spacer located along the outer periphery of the upper and lower recording surfaces an air gap thus being formed between the facing recording surfaces interior of the annular spacer.
FIG. 1 illustrates a conventional optical information record carrier 1 of the type to which the present invention obtains. The upper and lower optical disks of the carrier are designated by the reference letter a. An optical information record layer 2 is provided on each of the facing optical recording surfaces. An air gap is maintained between the optical disks a by an annular spacer b located about the outer periphery of the optical disks. The spacer is fixed to the disks a at the location shown in FIG. 1 by an adhesive 3.
The conventional process for assembling the carrier illustrated in FIG. 1 includes the following steps:
1. An optical disk (a) which is to form the lower disk in the carrier 1 is set on a support jig so that its information recording layer 2 faces upwardly. PA0 2. An adhesive 3 is supplied to the outer peripheral portion of the optical disk (a) in the support jig. PA0 3. The spacer (b) is then positioned on the adhesive 3 covering the peripheral portion of the optical disk (a). PA0 4. The adhesive 3 is thereafter also applied to the top of the spacer (b). PA0 5. The other optical disk (a), which is to form the upper disk, is positioned so that its peripheral portion is on the adhesive 3 covering the top of the spacer (b) and so that the information recording layer 2 of the upper optical disk faces downwardly. PA0 6. A weight is then put on the upper optical disk (a) so that the sandwich structure of two optical disks and a spacer therebetween is squeezed together until the adhesive 3 hardens.
A very serious problem with such a conventional structure may be explained as follows.
Before the adhesive 3 hardens, it is so soft that it tends to be pushed out of the area between the spacer and optical disks by the pressure of the weight. Therefore, if the adjoining surfaces of the optical disks (a) and the spacer (b) are completely flat, almost all of the adhesive 3 between these adjoining surfaces is pushed out, leaving at most only several microns of adhesive between the adjoining thickness of surfaces of each optical disk (a) and the spacer (b). This results in very poor adhesion between the disks and spacer, causing the disks to easily separate from the spacer.
If each optical disk (a) and/or the spacer (b) has a warp which cannot be corrected by the pressure of the weight, a gap will exist between the disk and the spacer so that a relatively thick layer of adhesive 3 will exist in the gap while at best only several microns of adhesive will exist between the disks and spacer at all other locations about the outer periphery of the disks. When the thickness of the adhesive 3 is only several microns, its adhesion power decreases markedly thus making it likely that the optical disks (a) and the spacer (b) will separate, even if a relatively thick layer of adhesive exists only in the gap produced by the warped section of the disk and/or the spacer.